Effect of Body Form and Response Threshold on the Vulnerability of Four Species of Teleost Prey Attacked by Largemouth Bass (Micropterus salmoides)

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Abstract
Experiments were performed using four prey species (fathead minnow, Pimephales promelas, largemouth bass, Micropterus salmoides, bluegill, Lepomis macrochirus, and tiger musky, Esox sp.) with various body and fin forms attacked by largemouth bass predators to determine how body and fin morphology, performance, and response thresholds influenced prey vulnerability. Prey differed in three factors that could affect the outcome of predator–prey interactions: body depth, the presence of spiny rays, and locomotor performance capability. Captures were only successful for strikes near the center of mass. The presence of spines was not shown to substantially affect predator strike targets on prey, but large body depth misdirected strikes from the center of mass area and increased the probability of prey escaping. Prey escape speeds were variable and not maximum. Acceleration rates in the startle response varied among the prey species. Tiger musky had the highest acceleration rates (11.7–12.2 m∙s−2). Acceleration rates decreased for the other prey in the order bluegill, largemouth bass, and fathead minnow. Predators attacking prey with higher acceleration performance were more likely to abort attacks and less likely to chase prey. Prey response thresholds were defined as the rate of change of the angle subtended by the predator as viewed by the prey at the start of the prey's motor response. This looming threshold varied among the species tested, and predators were more likely to abort attacks on prey with low thresholds. Low prey response thresholds correlated with high acceleration rates. The basis for multiple, rather than complementing, adaptations facilitating prey escape is not known, but may be related to risks and benefits during foraging by fish with different diets.